Current demands for high density and performance associated with ultra large scale integration of fabricated devices require submicron features, increased transistor and circuit speeds, and improved reliability. As semiconductor processes progress, pattern dimensions such as line width, and other types of critical dimensions, are continuously shrunken. Such demands require formation of device features with high precision and uniformity, which, in turn, necessitates careful monitoring of the fabrication process, including frequent and detailed inspections of the devices while they are still in the form of semiconductor wafers.
The term “specimen” used in this specification should be expansively construed to cover any kind of wafer, masks, and other structures, combinations and/or parts thereof used for manufacturing semiconductor integrated circuits, magnetic heads, flat panel displays, and other semiconductor-fabricated articles.
The term “inspection” used in this specification should be expansively construed to cover any kind of detection and/or classification of defects in a specimen provided by using non-destructive inspection tools or inspection machines. By way of non-limiting example, the inspection process can include generating an inspection recipe and/or runtime scanning (in a single or in multiple scans), reviewing, measuring and/or other operations provided with regard to the specimen or parts thereof using the same or different inspection tools. Note that, unless specifically stated otherwise, the term “inspection” or its derivatives used in this specification are not limited with respect to resolution or size of inspection area.
A variety of non-destructive inspection tools includes, by way of non-limiting example, scanning electron microscopes (SEM), tunneling electron microscope (TEM), atomic force microscopes (AFM), optical inspection tools, etc.
Repeating defects, repeater defects, and repeater are used interchangeably in this specification to refer to defects that are repetitively distributed at multiple locations on the specimen. Repeating defects are normally caused by a defect on a lithography mask or reticle, e.g., foreign particles or objects on the mask. After a wafer is printed with this kind of mask, the defects appear repetitively on certain dies of the wafer due to the repetitive usage of the mask during printing. For example, defects repeat at the same or substantially the same location in multiple dies (or every die) on the wafer.
A die-to-die (D2D) inspection is sometimes used for detecting repeating defects. In the die-to-die method, the presence or absence of a defect in a location is checked by comparing the pattern at the desired location in an inspected die with the pattern of the same location in another die, for example, a previously inspected die on the same wafer. A disadvantage of using a reference die for inspection is that, since the two locations in the inspected die and reference die are subjected to different variations, for example, process variations, mechanical and electrical variations, etc., such variations impose noise, which in some cases can be relatively high and can interfere with defect detection or decrease the sensitivity of defect detection. Such noise should be considered and disregarded, otherwise detection sensitivity and integrity are hindered. For instance, in a relatively noisy environment, the real repeating defects can be buried within noise and cannot be duly detected. This challenge increases as the design rules shrinks.
There is a need in the art for improving the sensitivity of detecting repeating defects.